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Biomedical subjects

S Clark

Publications and source records attributed to S Clark.

At least 325 records · Page 18Linked to original sources
PubMed1984

Absence of covalent binding by insulin to erythrocyte and reticulocyte insulin receptors.

We investigated whether insulin forms covalent bonds with its receptors on erythrocytes and reticulocytes, as it does in adipocytes (1). Of the [125I]-insulin specifically bound at 37 degrees C to human and rat erythrocytes and rat reticulocytes, only 1.5-2.3% was non-dissociable on extensive washing. When ghosts prepared from the washed cells were solubilized in Triton X-100, only 0.6-1.5% of the specifically bound radioactivity appeared in the void volume of a Sephadex G-50 column. Moreover in contrast to adipocytes, this high molecular weight radioactivity was not immunoprecipitable by antibodies to the insulin receptor and was dissociated during chromatography in sodium dodecyl sulphate. Thus we have been unable to demonstrate the formation of covalent bonds between insulin and its receptors on erythrocytes and reticulocytes. This finding is consistent with the hypothesis that covalent binding of insulin is a necessary receptor modification for insulin's metabolic effects.

Animals↗
PubMed1984

Group counseling in cardiac rehabilitation: effect on patient compliance.

A multicenter clinical trial was conducted to evaluate the effects on compliance of a group counseling program for cardiac patients and spouses. The sample comprised 58 couples in which one of the partners had documented atherosclerotic heart disease and was enrolled in an outpatient cardiac rehabilitation program. The experimental intervention involved a ten-week series of group sessions based on symbolic interactionist role theory. The research used a quasi-experimental, three-group, time-series design: Experimental group 1 consisted of 17 patients and their spouses who participated in group counseling; experimental group 2 consisted of 22 patients and their spouses, but only the patients participated in the group series; the control group consisted of 19 patients and their spouses who did not participate in the experimental program. Data were collected at baseline, ten weeks, and six months on four cardiac risk factors: weight loss, blood pressure, exercise, and smoking. Repeated measures analysis of variance showed a significant difference (P less than 0.01) in mean body fat among treatment groups, with experimental group 2 having the greatest decrease over time. Patients in both experimental groups demonstrated lowered blood pressure, with a significant decrease (P less than 0.05) in systolic blood pressure. Again, the largest decrease was in experimental group 2. Changes in weekly exercise level were not significantly different among groups, although the highest compliance was reported by experimental group 1 patients. Results support the efficacy of group counseling based on an interactionist role theory framework to increase compliance. The anticipated effect of spouse participation was not confirmed.

Counseling↗
PubMed1984

Pressor effects of brief and prolonged infusions of epinephrine in the conscious rat.

Plasma epinephrine may be increased in some patients with essential hypertension, and prolonged infusion of this catecholamine has been claimed to raise blood pressure. The objectives of our experiments were to determine whether continuous intravenous infusion of epinephrine raised blood pressure in a rat preparation known to respond in this way to angiotensin II in low dose and, if so, the plasma concentration of epinephrine required to raise pressure in comparison to the physiological range of plasma catecholamine concentration in the rat. Intravenous infusion of epinephrine at a rate of 400 ng X kg-1. min-1 or less for 30 min into Wistar rats did not increase mean arterial pressure (MAP); pressure did rise when the rate was increased to 800 ng X kg-1. min-1. However, when rats were given epinephrine at 400 ng X kg-1. min-1 for 4 days with continuous blood pressure recording, average MAP showed a progressive rise on successive days of infusion, reaching a maximum increase of 12 mmHg on the 4th and final day of infusion (P less than 0.02). Blood pressure did not change significantly during epinephrine infusion at 10 and 70 ng X kg-1. min-1. Plasma epinephrine was raised more than 13 times basal at the highest rate of infusion. In comparison, blood pressure and catecholamine concentrations increased only slightly although significantly during a period of restraint. We confirm the existence of a slowly developing pressor effect of epinephrine, but it is small and requires a large sustained increase of plasma epinephrine for its development.

Animals↗
PubMed1983

Disulfide exchange between insulin and its receptor. A possible post-binding step in insulin action.

A fraction of the insulin specifically bound to adipocytes undergoes a disulfide interchange with its receptor (Clark, S., and Harrison, L. C. (1982) J. Biol. Chem. 257, 12239-12244). In order to test the hypothesis that this covalent modification is a relevant step in insulin action, we have examined the relationship between disulfide binding of insulin and several insulin bioeffects, using sulfhydryl group blocking reagents as probes. The half-time of disappearance of disulfide linked insulin-receptor complexes (I-(S-S)-R) was rapid (4.5 min), consistent with their hypothesized role. A cell-impermeable reagent 5,5'-dithiobis(nitrobenzoic acid) (DTNB) had no effect on specific insulin binding but caused a dose-dependent decrease in both I-(S-S)-R and insulin-stimulated glucose transport. DTNB also inhibited the effect of insulin to stimulate glucose oxidation and to inhibit epinephrine-stimulated cyclic AMP production. In cultured IM-9 lymphocytes, insulin-induced down regulation of its receptor was decreased by 75% in the presence of 1 mM DTNB. Receptor antibodies stimulated adipocyte glucose transport maximally but their effect, unlike that of insulin, was not inhibited by DTNB. These findings suggest that receptor sulfhydryl groups are required for insulin action and support the notion that their interchange with insulin is a necessary step in activation of postreceptor pathways.

1-Methyl-3-isobutylxanthine↗
PubMed1983

Endogenous opioids: naloxone disrupts learned performance in rats.

The effect of naloxone on learned performance reinforced by food was examined in 2 experiments. Male rats were trained to run down a short runway for 5 (45 mg) food pellets per trial and were then shifted either to 1 or 0 pellets. Following such an abrupt reinforcement shift, animals typically show an emotional disruption of performance (Crespi, 1942) referred to as "depression". We examined the postshift depression-effect in groups treated either with saline (SAL) or naloxone (NAL). In experiment 1 NAL groups received a single 10 mg/kg (s.c.) injection prior to each postshift session. When compared with SAL controls, NAL animals showed an exaggerated postshift depression-effect. Furthermore, a single (0.3 mg/kg, s.c.) injection of the enkephalin analog FK 33-824 (D-Ala2, MePhe4, Met-(0)5-o1) produced a dramatic recovery of performance. In the second experiment, these effects were replicated at a low NAL dose (1 mg/kg), which had no direct effect on motor performance. These findings suggest that opiate systems may modulate the incentive motivation that maintains learned performance.

Animals↗
PubMed1983

Clinical characteristics of fibrositis. I. A "blinded," controlled study of symptoms and tender points.

Twenty-two patients with fibrositis, selected from a general medical outpatient population by a screening questionnaire and subsequent evaluation, were compared with age-, sex-, and clinic-matched patients without fibrositis. Although there was a high prevalence of musculoskeletal complaints in both groups, the fibrositis patients had a uniform constellation of symptoms, including axial pain, severe aching and stiffness, morning fatigue, and modulation by specific factors. They also had a higher incidence of tension headache and irritable bowel syndrome. The use of a dolorimeter demonstrated that fibrositis patients had many more areas of localized tenderness than control patients, but also that fibrositis patients did not have diffusely diminished pain threshold and tolerance. Using the criteria of this study, fibrositis appears to be a common and readily definable syndrome within the spectrum of soft tissue rheumatism.

Adolescent↗
PubMed1983

Methyl-directed repair of DNA base-pair mismatches in vitro.

An assay has been developed that permits analysis of DNA mismatch repair in cell-free extracts of Escherichia coli. The method relies on repair of heteroduplex molecules of f1 R229 DNA, which contain a base-pair mismatch within the single EcoRI site of the molecule. As observed with mismatch heteroduplexes of lambda DNA [Pukkila, P. J., Peterson, J., Herman, G., Modrich, P. & Meselson, M. (1983) Genetics, in press], in vivo mismatch correction of f1 heteroduplexes is directed by the state of dam methylation of d(G-A-T-C) sequences within the DNA duplex. Thus, the heteroduplex (formula: see book) is repaired in vivo to an EcoRI-sensitive form if the strand bearing the wild-type EcoRI sequence carries the dam modification and the other does not. Such molecules are also subject to mismatch repair by E. coli extracts. The in vitro activity is also dependent on ATP, the state of dam methylation of mismatch heteroduplexes, and products of mutH, mutL, mutS, and uvrE loci. However, crude fractions deficient in these gene products do complement in the cell-free system, thus providing assays for their isolation. The in vitro reaction is accompanied by repair synthesis on the unmethylated DNA strand.

Base Composition↗
PubMed1983

Airborne bacteria, endotoxin and fungi in dust in poultry and swine confinement buildings.

Airborne dust in swine and poultry confinements was analyzed to determine concentrations of total and gram-negative bacteria, total fungi, Aspergillus fumigatus and endotoxin. Airborne concentrations of total and gram-negative bacteria in swine and confinement units have been found to be as high as, or higher, than those found in other environments, such as wastewater treatment plants and cotton card rooms, where microbiologically contaminated organic dusts were present. Airborne endotoxin concentrations in the swine units (average 0.12 micrograms/m3) and poultry units (average 0.31 micrograms/m3) were in the range where clinical effects have occurred in other populations. Therefore, health studies of poultry and swine confinement workers with concurrent estimation of the individual daily exposure dose are warranted.

Air↗
PubMed1983

Training personnel in the prevention and management of violent behavior.

The authors describe a training program on prevention and management of violent behavior for the staff of a Veterans Administration hospital. The one-day workshop focuses on preventive identification of potentially violent situations and on methods of verbal and physical management of violent behavior. A study of workshop participants showed that trainees had improved knowledge about and performance in handling violent behavior after completing the program. Future developments in training in prevention and management of violent behavior should include greater availability of educational resource materials and incorporation of the subject in undergraduate and graduate health care training.

Humans↗
PubMed1982

Studies of thyroglobulin autoantibody synthesis using a micro-ELISA assay.

Thyroglobulin autoantibody synthesis by Hashimoto lymphocyte cultures has been studied using an ELISA, a plaque assay and tanned red cell haemagglutination. The ELISA system was found to be the most suitable and using this method IgG-class thyroglobulin antibody synthesis was detectable in cultures of mitogen-stimulated lymphocytes from all 10 Hashimoto patients studied, but not in cultures of lymphocytes from 4 normal donors. The ELISA was also sufficiently sensitive to detect thyroglobulin antibody synthesis in mitogen-free lymphocyte cultures from 4 out of the 10 Hashimoto patients and consequently it should be possible to use this system to study the effect of various pathophysiological factors on autoantibody synthesis which would otherwise be masked by mitogenic stimulation.

Adult↗
PubMed1982

Flow in coronary artery bypass grafts to totally and partially occluded left anterior descending coronary arteries.

Flow was determined by electromagnetic flowmeter in vein bypass grafts in 20 patients with a totally occluded left anterior descending (LAD) coronary artery and on 61 patients with a partially occluded LAD. The median flow in LAD grafts was 14.5 ml/min with total LAD occlusion, and 40 ml/min with partial LAD occlusion (p less than 0.001). In cases of total LAD occlusion, the presence of mild or moderate anteroseptal wall dysfunction was associated with more satisfactory flow than was the case with severe anteroseptal wall dysfunction (p less than 0.02). Flows over 25 ml/min were found only when the LAD distal to total occlusion was 1.5 mm or greater. Unsatisfactory flows were consistently found with total LAD occlusion, poor ventricular function, and a distal LAD less than 1.5 mm. Repeat catheterizations to determine an unsatisfactory patency rate under these conditions would be necessary to alter our policy of grafting all suitable vessels beyond a total occlusion.

Coronary Artery Bypass↗
PubMed1982

Analysis of histone gene expression during the cell cycle in HeLa cells by using cloned human histone genes.

Although it is generally agreed that histone protein synthesis is restricted to the S phase of the cell cycle--and therefore parallels DNA replication--both transcriptional and posttranscriptional levels of control have been invoked. Using blot hybridization with several cloned genomic human histone sequences representing different histone gene clusters as probes, we have assessed the steady-state level of histone RNAs in the nucleus and cytoplasm of G1 and S phase HeLa S3 cells. The representation of histone mRNA sequences of G1 compared with S phase cells was less than 1% in the cytoplasm and approximately 1% in the nucleus. These data are consistent with transcriptional control, but we cannot completely dismiss the possibility that regulation of histone gene expression is, to some extent, mediated posttranscriptionally. If histone gene transcription does occur in G1, the RNAs must either be rapidly degraded or be transcribed to a limited extent compared with S phase. An unexpected result was obtained when a blot of cytoplasmic RNA from G1 and S phase cells was hybridized with lambda HHG 41 DNA (containing H3 and H4 human genomic histone sequences). Although hybridization with histone mRNAs was observed for RNAs from S phase but not from G1 cells, hybridization with a nonhistone RNA of approximately 330 nucleotides present predominantly in G1 was also observed.

Bacteriophage lambda↗